GETTING STARTED

Type the name or coordinates of an object of interest into the "search box" at the top of the page and click on "search". If a name is used, the request is sent to the name resolver at NED (and then other services such as SIMBAD if not found), which returns the coordinates and an image size that are used for the search. Some examples might be:

M101	Most objects have a default search radius from NED
M87 r=1.0d	You can explicitly change the default search radius
Antennae	The resolver recognizes many names
14h03m12.6s +54d20m56.7s	If no radius is given a default of 0.2 degrees is used
14 03 12.6 54 20 56.7	Units are optional; equinox must be J2000
14:03.210 54:20.945	Many formats are accepted
180.468 -18.866 r=0.4	Default units are degrees in this case
Virgo Cluster	The object can be quite extended
0 0 r=180d	This example is related to an all-sky radius problem

There is also an "advanced search" button to the right that reveals more options for defining types of data to be returned (e.g., instruments; Data Products [e.g. best available, single exposure, combined, color images]). Note that "best available" selects the data product that is generally the most useful (e.g., the combined image, if it exists, rather than the single exposure or color image). There is also an Image Preference button.

The following table illustrates the type of available data that is in the HLA. Some are enhanced data products developed for the HLA while others are standard products available from the HST archives.

The tabs just below the search box provide three basic ways to view the results from the search:

INVENTORY (the default) - Shows the results in a table format. Click on the table heading to sort by that value (e.g., "ExpTime"). Clicking again on the same heading reverses the sort order. If there are more than 50 images found, there are controls to go through the table by pages or to jump to the first or last page.

Brief definitions of the table columns are provided at the bottom of the page; you can also get tool tips by placing your cursor on the column heading. By default not all of the (many) table columns are displayed. See instructions on the bottom right to add, remove, or reposition columns.

A subset of the inventory can be selected using the empty boxes under each column heading (e.g. *HRC* will select only ACS/HRC images). Move the cursor over the empty box for instructions.

The enhanced data products were generated from the original MAST data. The ACS and WFPC2 images have been combined using multidrizzle, aligned north up, and been astrometrically corrected when possible (i.e. approximately 80% of the cases; See the astrometric accuracy FAQ ). Clicking on the "Display" link in each row opens the interactive display for that image, while "download" allows you to download the FITS data.

When FITS images are not available in the HLA , the display and download options point to the MAST (Multimision Archive at Space Telescope) previews and data files.

IMAGES - Shows preview images of the results from the "search box" search (or cutouts if you have used the "advanced search" option). "Interactive Display" will open a FITS image if available in the HLA. "Mast Previews" will open the MAST preview in other cases. The image (FITS-Science or FITS-MEF; i.e., including only the science image , or including the image in Multi Extension Format with the science image in [1], the data quality array in extension [2], and the error array in extension [3].) There are two types of source lists available; DAOPHOT (primarily for point-like objects) and SExtractor (primarily for extended targets) and a plot button to show some basic plots, when available.

The "more" option in the bottom right provides a wide range of addition information including the proposal abstract, a list of what images went into the combined images, and a large number of working files which are briefly described here

FOOTPRINTS -Shows footprints of the results from the "search box" search (i.e., the outline of various detectors) on a Digital Sky Survey- 2 (DSS-2) image.

There are two important points to keep in mind when using footprints.

• Important point #1 - while we try to make the footprints as complete as possible, it is not possible to include 100% (e.g. we do not include planned observations). Proposers must therefore still use the MAST duplication tool to check for duplications.
• Important point #2 - To see the smallest apertures (e.g., FOS, GHRS, or NICMOS Grism) you may need to increase the scale. This is done by changing the radius using advanced search (down to a minimum of 0.01 degrees).
  

Selectable options for the footprint page include:

• which instruments to include
• whether to show the background image or not
• whether to include best available, single exposures or only combined images

A table with various information about each image is provided below the footprint image. You can either click on a table row to see the corresponding footprint, or on a footprint to show the corresponding table row. Selected datasets can also be highlighted  in the Inventory and Images, and will remain highlighted in all three views.

NICMOS GRISM - As its first HLA project, the ST-ECF is working on the extraction of a uniform set of NICMOS grism (G141) slitless spectra. A sample release of about 80% of the available fields are available as part of Data Release 1 via the NICMOS Grism Button or the interactive display. 

INTERACTIVE DISPLAY - You can look at an image or 2-dimensional spectrum more carefully, and overlay a source list, by using the "interactive display" (via either the inventory or images view). The image can be moved by either using the arrows in the upper left (< > ^ v) or by dragging the image using the mouse. The o button recenters. The + and - buttons zoom in or out. The Brighter and Darker buttons change the contrast. The "invert" button changes from white on black to black on white. SExtractor or DAOPHOT source lists from the image can be overlaid by clicking the appropriate box. A readout showing either the x-y position of the cursor, or wavelength at the "center" of the image for spectra is in the upper left. A line or column plot can be made at the location of the cursor by typing "L" or "C" especially useful for spectra. See the Help in the upper right of the interactive display for more details.

SOURCE LISTS - Two types of source lists are available via the HLA: DAOPHOT, which is optimized for point-like objects, and SExtractor, which is optimized for extended objects. In both cases the detection image is a "white light image" (i.e., a combination of images using all available filters within a single visit, also refered to as the "detection" image). The source lists can be overlaid on an image using the interactive display, and can be downloaded via the images view. The magnitudes are in the ABMAG system.  The detection threshold is roughly 5 sigma. Click here for the DAOPHOT source list document.

HELPFUL HINTS

-How to speed up the interactive display
The interactive display can become slow to refresh when moving around or zooming in or out when a source list is overlaid. Before zooming or moving, click the DAOPHOT or SExtractor box to remove the source list overlay. Once you are where you want to be, click the box again to add the overlay. This same technique is also useful for "blinking" the source lists.

KNOWN PROBLEMS

In the interest of making the HLA available to proposers at least one month before the cycle 17 proposal deadline we have scheduled Data Release 1 for February 8, 2008. There are still a few minor bugs we are working on, some of which  are listed below. We will update this list if any new items are found after the release.

- Availability of Source Lists
The availability of the source lists on the image page does not always match what is available in the interactive display. An example is that source lists may be advertised for the detection images but may not be present in the interactive display. Conversely, the color image may indicate that no source list is available to overlay when there actually is one.

-Radius searching:
The all-sky (0 0r=180) search for all instruments has been temporarily disabled. This feature will be restricted to radii of 45 degrees or less for a period following the initial release of Data Release 1. It still is possible to perform all-sky searches for single instruments.

UNDER THE HOOD

For each observation, the images have been grouped according to the filter in which they were obtained, and also according to which camera was used (eg., obsevations carried out with ACS could be obtained with either the WFC, HRC or SBC camera).

Each set of images (grouped by filter and camera) is then processed through the HLA pipeline using the Multidrizzle software (Koekemoer et al. 2002, HST Calibration Workshop, p.337) which corrects geometric distortion using the "drizzle" software (Fruchter and Hook 2002, PASP 114, 144), removes cosmic rays and combines the images. For the current release, the output pixel scale is set to be similar to the input pixel size (thus 0.05" for ACS/WFC, and 0.025" for ACS/HRC and ACS/SBC). Smaller pixel scales were precluded primarily on the basis of diskspace limitations, but are planned for a future release.

Each individual exposure, for all the filters used with a given camera, is first transformed separately to an undistorted output image, which are all registered to a common pixel grid (so that objects can be directly aligned on each image, even if dithering was used).

In addition, all the exposures for a given filter/camera combination are combined using Multidrizzle into a final, clean image for that filter/camera combination, which involves identification and removal of cosmic rays as well as astrometric alignment and distortion removal using "drizzle".

Finally, if more than one filter was used with a given camera during the observation, then the exposures from all these filters are combined into a single "total" image, as long as two or more exposures were obtained in each filter so that the cosmic ray masks obtained separately from each filter can be used. These "total" images can potentially be significantly deeper than the images obtained in each filter separately, and can be used as detection images with higher signal-to-noise than the individual filter images in most cases, although in some cases the combined image for each filter could also be used as a detection image. Images obtained with grisms or polarizer filters are excluded from the total image, although they are combined for each such spectral element separately.

FUTURE PRODUCTS

- A paper entitled "The Hubble Legacy Archive: General Description and Validation of Products" will be available. (~February 2008)

- Mosaics: Combined images using data from different visits to produce the deepest possible wide-field images

- A shopping cart so you can select and download several images at the same time

- An advanced search capability to allow you to select classes of objects (e.g., starbursts, irregulars, cepheids, ...)

- An All-HST-Sky Source List

RELATED VO SERVICES (e.g., VO SIAP services)

-To be updated March, 2008

ACKNOWLEDGEMENT FOR PUBLICATIONS

All refereed publications based on data obtained from the HLA must carry the following footnote:

Based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA) and the Canadian Astronomy Data Centre (CADC/NRC/CSA).

One copy of each paper resulting from data obtained from the HLA should be sent to the STScI.

In addition, publications of research supported by an ST ScI grant must carry the following acknowledgment:

Support for Program number  ____________ was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASAcontract NAS5-26555.